It is essential for normal breathing that the space within the pleural cavity surrounding the lungs be free of liquid and be subject to a negative pressure so as to draw the lungs outwardly to fill this pleural cavity in order to permit proper breathing. Any invasion of the pleural cavity such as caused by lung surgery or foreign objects which pierce the ribcage, or such as occur, for example, where the patient has pleurisy, generates fluids in the pleural cavity which tend to obstruct normal breathing. It is necessary to provide a device which can remove these fluids from the pleural cavity and at the same time ensure that the desired degree of negative pressure is maintained within the pleural cavity.
One of the basic types of apparatus which has been used for this purpose is shown, for example, in U.S. Pat. Nos. 3,363,626 and 3,363,627. This apparatus is known as an underwater drainage apparatus and provides three chambers, one chamber comprising a collection chamber for collecting the fluids drained from the pleural cavity through a thoracotomy tube, a second chamber known as an underwater seal chamber which protects the pleural cavity from being subject to atmospheric pressure, and a third chamber known as a pressure manometer chamber which serves to regulate the degree of negative pressure within the pleural cavity. This type of apparatus has been highly successful in both removing fluids from the pleural cavity and in maintaining the desired degree of negativity within the pleural cavity.
However, an apparatus such as disclosed in the patents referred to requires prefilling of the underwater seal chamber with water as well as prefilling the pressure manometer chamber to the desired level to maintain the desired degree of negativity within the pleural cavity. It is obvious that it would be desirable to eliminate the need for filling the underwater seal and manometer chambers particularly in emergency situations but also in general use, in that the less a user of the apparatus has to do with the operation the less likely it is that something will be done improperly, i.e. the greater the active participation the greater the chance for human error.
Although drainage devices have been developed which do not require a filling of the underwater seal chamber (see, for example, U.S. Pat. No. 4,015,603), these devices generally do not provide a direct indication of the suction force being exerted. Such a feature is, of course, highly desirable in a drainage device.